Cancer cells possess certain characteristics that allow them a growth advantage. These include six main alterations in cell physiology such as self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, evasion of apoptosis, indefinite proliferative potential, sustained angiogenesis, tissue invasion and metastasis (Hanahan and Weinberg, Cell, 2000, Vol. 100, 57-70). These changes are triggered by genomic instability and inflammation which generates a microenvironment conducive for tumor growth. In addition to the above mentioned traits, reprogramming of cellular energy metabolism and evasion of immune destruction has also been observed in a majority of cancers.
The enhanced survival in cancer cells is further potentiated by the presence of aberrantly activated signalling pathways. A large majority of cancers are known to have mutations in growth factor signalling cascades that lead to constitutive activation of these pathways. Such constitutive activations has been observed in growth factor receptors which include but are not limited to epidermal growth factor receptor—EGFR, fibroblast growth factor receptor—FGFR, Hepatocyte growth factor receptor—HGFR, etc. Furthermore, activating mutations have been reported in certain receptor as well as non receptor tyrosine kinases which include but are not limited to MET receptor tyrosine kinase, EGFR-tyrosine kinase, Bcr-Abl tyrosine kinase, Src tyrosine kinase etc. Activation of Ser-Thr kinases such as Ras and lipid kinases such as PI3-kinases also leads to oncogenesis. Chronic activation of the growth factor/cytokine/hormone-associated signalling leads to activation of immediate downstream components such as Src, Ras, PI3-kinase, etc. These kinases further activate effectors such as MEK, ERK, AKT, eventually leading to activation of transcription factors that endow the cells with a high proliferative potential, improved survival, subversion of metabolic pathways and inhibition of apoptosis. (Hanahan and Weinberg, Cell, 2000, Vol. 100, 57-70; Hanahan and Weinberg Cell 2011, Vol. 144, 646-674).
MEK kinase (Mitogen Activated Protein Kinase Kinase (MAPKK)) is an important component of the Ras-RAF-MEK-ERK cell survival pathway. The Ras pathway is activated by binding of growth factors, cytokines, and hormones to their cognate receptors. In cancer cells, this pathway is, however, constitutively activated and leads to increased cancer cell survival, cell proliferation, angiogenesis and metastasis. The tumors that show constitutive activation of the Ras or the MEK kinase include but are not limited to those of the colon, pancreas, breast, brain, ovary, lungs and skin (Sebolt-Leopold and Herrera, Nat. Rev. Cancer 2004, 4 937-947; Fukazawa et al., Mol. Cancer Ther. 2002, Vol. 1, 303-309). Activation of Ras (due to upstream signalling or as a result of activating point mutations in the Ras oncogene) lead to the phosphorylation and activation of Raf kinase that in turn phosphorylate and activate MEK kinase. MEK1/2 kinase phosphorylates and activates the ERK1/2 kinase (also referred to as MAP Kinase) that further phosphorylates and regulates the function of proteins such as Mcl-1, Bim and Bad that are involved in cell survival and apoptosis. Thus, activation of this phosphorylation mediated cascade leads to enhanced cell proliferation, cell survival, decreased cell death that are necessary for initiation and maintenance of the tumorigenic phenotype (Curr. Opin. Invest. Drugs, 2008, 9, 614).
The Ras-Raf-MEK-ERK cascade plays a pivotal role in survival and proliferation of cancer cells. As such, inhibition of this pathway at any of these levels would lead to the inhibition of cancer cell growth, proliferation and survival. Indeed, it has already been reported that inhibition of Ras or Raf leads to inhibition of tumor growth in animal models as well as in cancer patients. However, the success with these inhibitors has been limited to only certain types of cancers (e.g. Sorafenib which inhibits Raf kinase has been approved for renal cell carcinoma). Hence, inhibiting MEK is a novel approach towards controlling this pathway in cancer cells. Moreover, the possibility of designing allosteric inhibitors also allows enhanced selectivity that is crucial for decreasing the toxic effects associated with kinase inhibitors.
The MEK-ERK Pathway is activated in numerous inflammatory conditions (Kyriakis and Avruch, 1996, Vol. 271, No. 40, pp. 24313-24316; Hammaker et al., J. Immunol. 2004, 172, 1612-1618), including rheumatoid arthritis, inflammatory bowel disease and COPD. MEK regulates the biosynthesis of the inflammatory cytokines TNF, IL-6 and IL-1. It has been shown that MEK inhibitors interfere with the production/secretion of these cytokines. Array BioPharma has developed a first-in-class MEK inhibitor (ARRY 438162) and initiated clinical trials in rheumatoid arthritis (RA) patients.
International patent applications WO/2003/053960, WO/2005/023251, WO/2005/121142, WO/2005/051906, WO/2010/121646 describe MEK inhibitors.